1. Field of the Invention
This invention relates to breathable gas supply apparatus, and particularly but not exclusively to such apparatus for use in Continuous Positive Airway Pressure (CPAP) treatment of conditions such as Obstructive Sleep Apnea (OSA) and other respiratory disorders and diseases such as emphysema. It will be described herein in its application to CPAP treatment apparatus, but it is to be understood that the features of the invention will have application to other fields of application, such as mechanical ventilation and assisted respiration.
2. Description of Related Art
CPAP treatment of OSA, a form of Noninvasive Positive Pressure Ventilation (NIPPV), involves the delivery of a pressurised breathable gas, usually air, to a patient's airways using a conduit and mask. Gas pressures employed for CPAP typically range from 4 cm H2O to 28 cm H2O, at flow rates of up to 180 L/min (measured at the mask), depending on patient requirements. The pressurised gas acts as a pneumatic splint for the patient's airway, preventing airway collapse, especially during the inspiratory phase of respiration.
CPAP machines comprising an air flow generator for supplying pressurised air to the patient are known, and over recent years there has been commercial imperative for more compact CPAP machines. However, in seeking to reduce the size of the CPAP machines there has been a trade-off between reduced size on the one hand and reduced performance and/or increased noise on the other, for example Malinckrodt/Tyco/Puritan Bennett ‘Goodnight’ Series.
The advantages of incorporating humidification of the air supply to a patient are known, and CPAP machines are known which incorporate humidifying devices, either separately from the flow generator or integrated therewith. An example of an integrated flow generator/humidifier unit is the ResMed® S7 sold by the present Applicant.
Another problem with some flow generators is extensive use of foam in the air path for sound absorption. The foam can degrade with time.